Cartons are used in a variety of industries, for example, the food industry. Cartons which may be collapsed or knocked-down are especially desirable as they may be shipped or stored in a flat configuration, thereby minimizing the amount of storage space used. Cartons which are reusable after being disassembled or knocked-down reduce both the waste and expense associated with the manufacture of new or replacement cartons.
Some cartons are assembled using glue, staples or stitching to secure the bottom flaps. U.S. Pat. Nos. 2,713,454 and 2,747,788, for example, disclose cartons which close or secure the bottom flaps with glue or other adhesive materials. The glued flaps form a strong and durable seal. However, the glue also makes disassembly and reuse of the cartons difficult, if not impossible. Moreover, repeated disengagement of glued or otherwise secured bottom flaps from each other weakens the integrity of the flaps and shortens the useful life of the carton.
Other cartons utilize tabs and slots on end and side flaps to close and secure the bottoms and tops of the cartons. For example, U.S. Pat. Nos. 490,167 and 4,884,741 disclose cartons with top and bottom closures which are secured by inserting tabs on end flaps into slots on adjacent side flaps, and U.S. Pat. Nos. 4,279,379 and 4,702,408 disclose cartons with bottom flaps or panels which are locked by pushing tabs into slots to join end flaps and side flaps together. Such cartons may be disassembled and reused. However, when products or articles are placed in such cartons, the products can inadvertently disengage the inserted tabs from the slots at the bottom of the carton, thereby weakening or eliminating the bottom closure. In addition, the tabs may bend or their rigidity may be diminished by repeated assembly or disassembly of the carton.
Still other cartons, for example, U.S. Pat. Nos 5,046,662, 5,104,035 and 4,884,741 disclose self-locking cartons which utilize flaps containing fold lines and locking recesses or slots, to interlock with tabs. A fold on an end flap which parallels the outer edge of the flap permits the flap to be folded in an outwardly direction, away from the carton interior. The folding effectively shortens the end flap, thereby making it easier to insert the tabs of the end flap into the slots or locking recesses of adjacent side flaps. If locking recesses are used instead of slots, they shield the tabs in the interior of the carton and help to prevent inadvertent disengagement of the tabs. However, conventional end flap fold lines create other problems. For example, because the fold lines are biased outwardly, away from the interior of the carton, the fold lines increase the likelihood that the tabs will inadvertently disengage from the slots or locking recesses. Also, assembling and disassembling the closures of such cartons require several steps.
A need, therefore, exists for a reusable carton with a strong and positive self-locking bottom closure which is easy to lock and unlock and is not susceptible to inadvertent opening or disengagement.